Hurricane Harvey Has Unleashed Hordes Of Floating Fire Ants

A red invasive fire ant, Solenopsis invicta. They have been in the United States since the 1930s.

When flooding occurs, these ants know how to organize.

Fire ants are a common scourge in Texas and other places around the United States, but Solenopsis invicta is actually an invasive species from the rainforests of Brazil. While a single ant might struggle to float, when fire ants organize into colonies and utilize surface tension, they form sort of a waterproof “fabric”.

“This rafting is thought to be an adaptive behavior to withstand this kind of environmental pressure. The colony can raft to a safe location or hold out until the flooding subsists,” says Phil Barden, an entomologist from New Jersey Institute of Technology. He adds they likely developed this adaptive behavior because they were used to wet environments in the rainforests of South America.

They form the rafts by linking up their tiny legs and mouthparts to form a floating mat. The whole colony is taken along for the ride—including the queen. The ants form this raft without any overall guidance, in a process called self-assembly.

The floating mats also self-heal. When ants are removed, others will quickly move in to take their place. This way, they can potentially float for weeks. Soapy water trumps fire ants, though. Soap and other surfactants change the surface tension of the water and completely prevent them from floating.

When humans get stung by fire ants, it can be a very painful experience. To add more drama on top of an already difficult problem, Texas residents dealing with flooding now need to worry about running into piles of stinging insects.

Shaena Montanari is a paleontologist and science communicator. Follow her on Twitter at @DrShaena for the latest natural history and fossil news.